Technical Field
This document discloses a joint between a turbine disk and a shaft of a turbocharger that reduces heat transfer from the turbine disk to the shaft.
Description of the Related Art
Turbochargers increase the power density of an internal combustion engine by compressing the air entering the intake manifold of the engine. Turbochargers include a turbine and a compressor. The turbine may include a turbine inlet and outlet duct that surrounds a turbine disk. The turbine disk may be connected to a plurality of turbine blades or the disk and blades may be unitary in structure and referred to as a blisk. The compressor may include a compressor housing that surrounds a compressor disk. A common shaft may connect the compressor disk to the turbine disk. A flow of exhaust gas from the engine proceeds through an exhaust manifold to the turbine inlet duct, which imparts rotation to the turbine disk, the shaft and the compressor disk. As the compressor disk spins, fresh air is compressed and forced into the intake manifold of the engine thereby boosting the power density of the engine. The shaft connecting the turbine disk to the compressor disk typically passes through a journal bearing and a lubricating oil bath.
Heat from the exhaust gas creates high operating temperatures for turbocharger components, especially the turbine blades, which readily transfer heat to the turbine disk. The high operating temperature of the turbine disk needs to be attenuated before it is communicated to the lubricating oil bath and the journal bearing. One method to achieve this attenuation is to provide a pocket or cavity between the turbine disk and the shaft as disclosed in U.S. Pat. No. 7,241,416. However, this technique leads to reduced strength at the joint between the turbine disk and the shaft and it further undermines the capability of the turbine disk to withstand a severe loading event, such as a blade loss. Accordingly, there is a need for a turbine disk/shaft connection that reduces heat transfer from the turbine disk to the shaft, the journal bearing and the oil bath without compromising the structural integrity of the turbine disk/shaft connection.